full_basic_decodec.c

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <stdio.h>
#include <stdarg.h>

void logging(const char *fmt, ...);

int main(int argc, const char *argv[])
{
  av_register_all();

  AVFormatContext *pFormatContext = avformat_alloc_context();
  if (!pFormatContext) {
    logging("ERROR could not allocate memory for Format Context");
    return -1;
  }

  if (avformat_open_input(&pFormatContext, argv[1], NULL, NULL) != 0)
  {
    logging("ERROR could not open the file");
    return -1;
  }

  if (avformat_find_stream_info(pFormatContext, NULL) < 0)
  {
    logging("ERROR could not get the stream info");
    return -1;
  }

  AVCodec *pCodec = NULL;
  AVStream *pStream = NULL;
  int video_stream_index = -1;

  // find the first video stream
  for (int i = 0; i < pFormatContext->nb_streams; i++)
  {
    video_stream_index = i;
    pStream = pFormatContext->streams[i];
    AVCodecParameters *pCodecParameters =  pStream->codecpar;

    // https://ffmpeg.org/doxygen/trunk/group__lavu__misc.html#gga9a84bba4713dfced21a1a56163be1f48ac1a46f59be5c6c2d3412ab172d6b8cf5
    if (pCodecParameters->codec_type == AVMEDIA_TYPE_VIDEO) {
      pCodec = avcodec_find_decoder(pCodecParameters->codec_id);

      if (pCodec==NULL)
      {
        logging("ERROR unsupported codec!");
        return -1;
      }

      break;
    }
  }
  // https://ffmpeg.org/doxygen/trunk/structAVCodecContext.html
  AVCodecContext *pCodecContext = avcodec_alloc_context3(pCodec);
  if (!pCodecContext) {
    logging("failed to allocated memory for AVCodecContext");
    return -1;
  }

  if (avcodec_open2(pCodecContext, pCodec, NULL) < 0) {
    logging("failed to open codec through avcodec_open2");
    return -1;
  }

  // https://ffmpeg.org/doxygen/trunk/structAVFrame.html
  AVFrame *pFrame = av_frame_alloc(); // pict_type, )ts
  if (!pFrame) {
    logging("failed to allocated memory for AVFrame");
    return -1;
  }
  // https://ffmpeg.org/doxygen/trunk/structAVPacket.html
  AVPacket *pPacket = av_packet_alloc(); // pts, dts, duration
  if (!pPacket) {
    logging("failed to allocated memory for AVPacket");
    return -1;
  }

  while (av_read_frame(pFormatContext, pPacket) >= 0) {

    int response = avcodec_send_packet(pCodecContext, pPacket);
    if (response < 0) {
      logging("error sending packet");
      return -1;
    }

    while (response >= 0) {
      response = avcodec_receive_frame(pCodecContext, pFrame);

      if (response == AVERROR(EAGAIN) || response == AVERROR_EOF) {
        logging("error receiving frame");
        return -1;
      } else if (response < 0) {
        fprintf(stderr, "Error during decoding\n");
        exit(1);
      }
      printf("saving frame %3d\n", pCodecContext->frame_number);
    }
  }





  logging("releasing all the resources");

  avformat_close_input(&pFormatContext);
  avformat_free_context(pFormatContext);
  av_packet_free(&pPacket);
  av_frame_free(&pFrame);
  avcodec_free_context(&pCodecContext);
  return 0;
}

void logging(const char *fmt, ...)
{
    va_list args;
    fprintf( stderr, "LOG: " );
    va_start( args, fmt );
    vfprintf( stderr, fmt, args );
    va_end( args );
    fprintf( stderr, "\n" );
}